RESUMO
Native Americans domesticated maize (Zea mays ssp. mays) from lowland teosinte parviglumis (Zea mays ssp. parviglumis) in the warm Mexican southwest and brought it to the highlands of Mexico and South America where it was exposed to lower temperatures that imposed strong selection on flowering time. Phospholipids are important metabolites in plant responses to low-temperature and phosphorus availability and have been suggested to influence flowering time. Here, we combined linkage mapping with genome scans to identify High PhosphatidylCholine 1 (HPC1), a gene that encodes a phospholipase A1 enzyme, as a major driver of phospholipid variation in highland maize. Common garden experiments demonstrated strong genotype-by-environment interactions associated with variation at HPC1, with the highland HPC1 allele leading to higher fitness in highlands, possibly by hastening flowering. The highland maize HPC1 variant resulted in impaired function of the encoded protein due to a polymorphism in a highly conserved sequence. A meta-analysis across HPC1 orthologs indicated a strong association between the identity of the amino acid at this position and optimal growth in prokaryotes. Mutagenesis of HPC1 via genome editing validated its role in regulating phospholipid metabolism. Finally, we showed that the highland HPC1 allele entered cultivated maize by introgression from the wild highland teosinte Zea mays ssp. mexicana and has been maintained in maize breeding lines from the Northern United States, Canada, and Europe. Thus, HPC1 introgressed from teosinte mexicana underlies a large metabolic QTL that modulates phosphatidylcholine levels and has an adaptive effect at least in part via induction of early flowering time.
Assuntos
Adaptação Fisiológica , Flores , Interação Gene-Ambiente , Fosfatidilcolinas , Fosfolipases A1 , Proteínas de Plantas , Zea mays , Alelos , Mapeamento Cromossômico , Flores/genética , Flores/metabolismo , Genes de Plantas , Ligação Genética , Fosfatidilcolinas/metabolismo , Fosfolipases A1/classificação , Fosfolipases A1/genética , Fosfolipases A1/metabolismo , Proteínas de Plantas/classificação , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Zea mays/genética , Zea mays/crescimento & desenvolvimentoRESUMO
PREMISE OF THE STUDY: Plants and animals may experience reproductive Allee effects in fragmented populations, and obligate pollination mutualisms may be especially sensitive to extinction risk via this density-dependent process. In this study we examine how a shift from within-crown reproductive synchrony to asynchrony influences reproductive assurance through contributions to selfing and outcrossing in small, spatially isolated populations of Ficus. METHODS: The research focuses on the monoecious fig F. petiolaris and consists of phenological analyses and genetic assessments of selfing and outcrossing for populations located in Baja California's Sonoran Desert. KEY RESULTS: Phenological censuses of eight populations revealed within-crown asynchrony in 44% of reproducing trees, with 16% having sufficient overlap of male and female flowering phases to permit selfing via the cycling of pollinating fig wasps within natal trees. In mating system analyses of two of these populations, however, multilocus outcrossing rates (t(m)) were indistinguishable from 1. This result, combined with low levels of inbreeding, indicates selfing to be absent or at best a minor contributor to reproductive assurance. CONCLUSIONS: The results indicate that the fitness benefits of within-crown asynchrony lie not with selfing, as commonly asserted, but with increased opportunities for outcross pollen transmission and receipt, changing our understanding of the mechanisms by which reproduction is facilitated and extinction risk minimized in naturally fragmented Ficus populations. Given the role of fig fruit as a keystone food resource in many tropical environments, trait variation leading to reproductive assurance in figs, such as within-crown asynchrony, has broader ecosystem-level implications.